Insights into g-C₃N₄as a chemi-resistive gas sensor for VOCs and humidity-a review of the state of the art and recent advancements

Over the past decades, many materials like metal oxides, conducting polymers, carbon nanotubes, 2D materials, graphene, zeolites and porous organic frameworks (MOFs and COFs) have been explored for chemo-sensing applications owing to their unique properties. One such 2D material in the center of attraction in recent years is graphitic polymeric carbon nitride, g-CN (so-called g-C3N4). It has emerged as a potential candidate for chemo-sensing applications due to its facile synthesis, physicochemical properties, and tunable electronic structures. Though there are a few reports and reviews available for various other sensing principles of g-C3N4, such as photo-electrochemical, electrochemiluminescence, electrochemical and fluorescence-based ion-sensing and bio-sensing, it is difficult to find a comprehensive review solely on the chemi-resistive gas sensing signatures of g-C3N4. This stood out as our first and foremost inspiration to compile this review by focusing on chemi-resistive sensors reported using g-C3N4 and its composites. In this review, the humidity and VOC sensing applications of g-C3N4 & its composites have been accentuated. A detailed sensing mechanism, along with the specific rationales for selective detection, has been presented. Along with the specific figures of merit of the g-C3N4 based chemo-sensors, a futuristic perspective of carbon nitride-based hybrid materials and key strategies to improve the sensing characteristics are presented. Thus, this progress in the recently booming g-C3N4 and its hybrid-based chemo-sensors paves a way to further fabricate different forms of g-C3N4 based sensors for the challenges ahead in the field of energy and environment, especially IoT based futuristic sensing platforms.